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From:   Imran Khan <imran.f.khan@oracle.com>
To:     tj@kernel.org, viro@zeniv.linux.org.uk, gregkh@linuxfoundation.org,
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Cc:     linux-kernel@vger.kernel.org
Subject: [PATCH v8 04/10] kernfs: Introduce interface to access global kernfs_open_file_mutex.
Date:   Sun, 10 Apr 2022 12:37:13 +1000
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This allows to change underlying mutex locking, without needing to change
the users of the lock. For example next patch modifies this interface to
use hashed mutexes in place of a single global kernfs_open_file_mutex.

Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
---
 fs/kernfs/file.c | 42 +++++++++++++++++++++++++++++++-----------
 1 file changed, 31 insertions(+), 11 deletions(-)

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index c89220dcfdc1..214b48d59148 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -47,6 +47,22 @@ struct kernfs_open_node {
 #define attribute_to_node(ptr, type, member)	\
 	container_of(ptr, type, member)
 
+static inline struct mutex *kernfs_open_file_mutex_ptr(struct kernfs_node *kn)
+{
+	return &kernfs_open_file_mutex;
+}
+
+static inline struct mutex *kernfs_open_file_mutex_lock(struct kernfs_node *kn)
+{
+	struct mutex *lock;
+
+	lock = kernfs_open_file_mutex_ptr(kn);
+
+	mutex_lock(lock);
+
+	return lock;
+}
+
 static DEFINE_SPINLOCK(kernfs_notify_lock);
 static LLIST_HEAD(kernfs_notify_list);
 
@@ -520,8 +536,9 @@ static int kernfs_get_open_node(struct kernfs_node *kn,
 				struct kernfs_open_file *of)
 {
 	struct kernfs_open_node *on, *new_on = NULL;
+	struct mutex *mutex = NULL;
 
-	mutex_lock(&kernfs_open_file_mutex);
+	mutex = kernfs_open_file_mutex_lock(kn);
 
 	/**
 	 * ->attr.open changes under kernfs_open_file_mutex so we don't
@@ -531,13 +548,13 @@ static int kernfs_get_open_node(struct kernfs_node *kn,
 				   lockdep_is_held(&kernfs_open_file_mutex));
 	if (on) {
 		list_add_tail(&of->list, &on->files);
-		mutex_unlock(&kernfs_open_file_mutex);
+		mutex_unlock(mutex);
 		return 0;
 	} else {
 		/* not there, initialize a new one and retry */
 		new_on = kmalloc(sizeof(*new_on), GFP_KERNEL);
 		if (!new_on) {
-			mutex_unlock(&kernfs_open_file_mutex);
+			mutex_unlock(mutex);
 			return -ENOMEM;
 		}
 		atomic_set(&new_on->event, 1);
@@ -546,7 +563,7 @@ static int kernfs_get_open_node(struct kernfs_node *kn,
 		list_add_tail(&of->list, &new_on->files);
 		rcu_assign_pointer(kn->attr.open, new_on);
 	}
-	mutex_unlock(&kernfs_open_file_mutex);
+	mutex_unlock(mutex);
 
 	return 0;
 }
@@ -567,12 +584,13 @@ static void kernfs_put_open_node(struct kernfs_node *kn,
 				 struct kernfs_open_file *of)
 {
 	struct kernfs_open_node *on;
+	struct mutex *mutex = NULL;
 
 	/* ->attr.open NULL means there are no more open files */
 	if (rcu_dereference_raw(kn->attr.open) == NULL)
 		return;
 
-	mutex_lock(&kernfs_open_file_mutex);
+	mutex = kernfs_open_file_mutex_lock(kn);
 
 	on = rcu_dereference_protected(kn->attr.open,
 				       lockdep_is_held(&kernfs_open_file_mutex));
@@ -589,7 +607,7 @@ static void kernfs_put_open_node(struct kernfs_node *kn,
 		rcu_assign_pointer(kn->attr.open, NULL);
 		kfree_rcu(on, rcu_head);
 	}
-	mutex_unlock(&kernfs_open_file_mutex);
+	mutex_unlock(mutex);
 }
 
 static int kernfs_fop_open(struct inode *inode, struct file *file)
@@ -731,7 +749,7 @@ static void kernfs_release_file(struct kernfs_node *kn,
 	 * here because drain path may be called from places which can
 	 * cause circular dependency.
 	 */
-	lockdep_assert_held(&kernfs_open_file_mutex);
+	lockdep_assert_held(kernfs_open_file_mutex_ptr(kn));
 
 	if (!of->released) {
 		/*
@@ -748,11 +766,12 @@ static int kernfs_fop_release(struct inode *inode, struct file *filp)
 {
 	struct kernfs_node *kn = inode->i_private;
 	struct kernfs_open_file *of = kernfs_of(filp);
+	struct mutex *mutex = NULL;
 
 	if (kn->flags & KERNFS_HAS_RELEASE) {
-		mutex_lock(&kernfs_open_file_mutex);
+		mutex = kernfs_open_file_mutex_lock(kn);
 		kernfs_release_file(kn, of);
-		mutex_unlock(&kernfs_open_file_mutex);
+		mutex_unlock(mutex);
 	}
 
 	kernfs_put_open_node(kn, of);
@@ -767,6 +786,7 @@ void kernfs_drain_open_files(struct kernfs_node *kn)
 {
 	struct kernfs_open_node *on;
 	struct kernfs_open_file *of;
+	struct mutex *mutex = NULL;
 
 	if (!(kn->flags & (KERNFS_HAS_MMAP | KERNFS_HAS_RELEASE)))
 		return;
@@ -774,7 +794,7 @@ void kernfs_drain_open_files(struct kernfs_node *kn)
 	if (rcu_dereference_raw(kn->attr.open) == NULL)
 		return;
 
-	mutex_lock(&kernfs_open_file_mutex);
+	mutex = kernfs_open_file_mutex_lock(kn);
 	on = rcu_dereference_check(kn->attr.open,
 				   lockdep_is_held(&kernfs_open_file_mutex));
 	if (!on) {
@@ -792,7 +812,7 @@ void kernfs_drain_open_files(struct kernfs_node *kn)
 			kernfs_release_file(kn, of);
 	}
 
-	mutex_unlock(&kernfs_open_file_mutex);
+	mutex_unlock(mutex);
 }
 
 /*
-- 
2.30.2